Insane dashcam footage has shows the moment some speeding madman drove straight up a bus lane, before quickly changing lanes and smashing into multiple cars on an Auckland motorway on Monday afternoon.

Ben Comemadang was driving home from work on the Southern Motorway, when his dashcam caught a driver flying past and smashing into the back of a white Mazda.

"The car was going well over 100 and at first looked like it was going to hit the back of the bus, but then it swooped to the side into the back of the SUV," Comemadang told Newshub.

He said the SUV then spun out in front of the bus and ended up in a roadside bush, but the speedster kept driving.

"At least three cars were hit, the video shows two being crashed into, then the speeding car ended up in the bushes as well."

He said he pulled over to check on the driver and passenger of the white Mazda, who were both in shock.

"The passenger came out of the car and was shaking, in shock. Then I went to see the driver who was panicking and crying. I told her she'd better get out [of the car] because I smelled gas."

On ya Ben!

The driver of the speeding car is reportedly in hospital undergoing testing and told police they did not remember anything about the incident.